This invention relates to color compositions for use in a wide variety of coloring applications. In particular, the invention relates to mixtures of pigments capable of producing consistent, compatible and predictable color effects. The invention relates further to a method of mixing the pigments in order to achieve the desired color effects.
Common, reflected, non-luminescent color compositions or pigments are visible to the eye because certain wavelenths of light impinging thereon are absorbed and the remaining wavelengths, representing the color observed, are selectively reflected towards the observer. While different lighting conditions may cause the apparent color to vary, the reflected portion of the light which illuminates the common color composition is that which is received by the observer and is preceived as color.
Luminescent color compositions or pigments, for example, fluorescent and phosphorescent pigments, are those which absorb incident illuminating radiation and re-emit the absorbed radiation at the same or a different wavelength. The light which illuminates the phosphorescent or fluorescent pigment is different from the light which is received by the observer because it has been absorbed and re-emitted.
The difference between common pigments and luminescent pigments can be characterized somewhat in terms of light intensity and brilliance. More importantly, for purposes of this disclosure, the difference between common and luminescent pigments is that common pigments selectively remove or absorb illuminating radiation and luminescent pigments transmit certain wavelengths. The absorption phenomenon is sometimes referred to hereinafter as the subtractive aspect of a color composition or pigment because certain wavelengths are removed or absorbed from incoming radiation and thus never reach the observer. The transmissive effect of luminescent pigments is sometimes hereinafter referred to as the additive aspect of a color composition because the illuminating radiation, although possibly changed in wavelength, is transmitted to the observer and multiple wavelengths combine to produce the observed color.
Common pigments reflect certain wavelengths and require a source of illuminating radiation to be visible.
Luminescent materials may be divided into two general catagories; that is, fluorescent materials and phosphorescent materials. Fluorescent materials are characterized by a relatively short time, for example, 10.sup.-8 seconds between absorption of illuminating radiation and re-emission. Fluorescent materials produce vivid colors which appear to glow-in-the-daylight.
Phosphorescent materials are characterized by a time greater than 10.sup.-8 seconds between absorption and re-emission. Phosphorescent materials, in effect, store the energy of the incident radiation and re-emit it over a longer time so that phosphorescent materials appear to glow in the absence of illuminating radiation, i.e., they glow-in-the-dark.
Common pigments are available for use in an almost unlimited variety of colors, shades, hues and intensities. Fluorescent pigments are likewise available in a rather large variety of colors, although less than the common type. Phosphorescent pigments are available in a rather limited palette of colors.
In the past, it has not been possible to produce a palette of coloring compositions that glow-in-the-dark. While some variations of color have been produced, as in Gravisse, U.S. Pat. No. 4,208,300 and Gravisse et al., U.S. Pat. No. 4,211,813, there is no teaching of how the compositions may be mixed or combined to produce a desired result in a wide variety of palette of colors. In Gravisse, for example, there is only a rought approximation of the daylight-visible and night-visible colors and there is no explanation of any method of controlling, in a precise manner, the resulting color effect. Gravisse et al., like Gravisse, uses fluorescent and phosphorescent materials to produce various color effects. In one example, Gravisse et al. also discloses the use of a common color, although in a layered fashion and not mixed with the phosphorescent and fluorescent colors.
The present invention teaches how it is possible to mix, compatibly, common and luminescent pigments so that the color effects may be accurately predicted and controlled.
Of importance to the understanding of the present invention, it is a fact that it has been discovered that color pigments may be characterized by their additive or transmissive aspect or by their subtractive or absorptive/reflective aspect. When the wavelengths of the emitted light combine, the effect is said to be additive. When wavelengths of the illuminating radiation are absorbed and only selectively reflected, the effect is said to be subtractive.
Primary colors are those which, when mixed together, produce other colors. The primary additive colors are RED, BLUE and GREEN. The primary subtractive colors are RED, YELLOW and BLUE. The primary colors mentioned also have compliments which, when combined in accordance with the teachings of the present invention, will produce other colors. However for purposes of this disclosure, the above mentioned primary colors will be discussed exclusively.
While there is some theoretical basis for a four-color primary system using RED, YELLOW, GREEN and BLUE, a practical system has not been developed which takes cognizance of both the additive and the subtractive aspects of primary colors. In other words, either colors are mixed additively by the combination of various wavelengths of light, or they are mixed subtractively so that selected wavelengths may be removed or absorbed and other wavelengths may be reflected.
It is an aspect of the present invention that a system and method of coloration had been developed which allows colors to be mixed both additively and subtractively. Additive aspects are accounted for separately from subtractive aspects, but certain rules of mixing are observed to prevent undesirable loss of color or browning.